1. Field of the Invention
The present invention relates to transmissive dimension measuring devices and, more particularly, relates to an optical type transmissive dimension measuring device which detects a change in amount of light by an optical receiver when an object to be measured shields outgoing light from a projector, thereby measuring various kinds of dimensions of the object to be measured.
2. Description of the Related Art
Conventionally, an optical type transmissive dimension measuring device has been used to detect, for example, an outer diameter, position, and interval of an object. The optical type transmissive dimension measuring device includes a projector which projects parallel light to an area to be measured and an optical receiver which receives light transmitted through the area to be measured; and the optical type transmissive dimension measuring device measures a length of shade of the object to be measured, which is generated by shielding the parallel light by the object to be measured and measures various kinds of dimensions of the object to be measured based on an amount of received light received by the optical receiver.
The principle of operation of the optical type dimension measuring devices is largely divided into two methods: a CCD method and a scanning method. In the CCD method, light emitted from a light emitting element is converted to parallel light by a light projecting lens; and the parallel light is radiated to a dimension measuring range. The optical receiver receives light from the dimension measuring range by an incorporated one-dimensional CCD image sensor. When the object to be measured shields the parallel light, shade proportional to the size of a light shielding area is generated at a light receiving unit; and various kinds of dimensions of the object to be measured are calculated based on the size and position of the shade and are outputted.
Furthermore, in the scanning method, light emitted from a light emitting element is deflected by a deflecting element such as a polygon mirror, the deflected light is converted to a parallel light beam by a collimator lens, and is radiated to a dimension measuring range. Light which scans an object to be measured in the dimension measuring range is converged by a light receiving lens in the inside of an optical receiver and is converted to an electrical signal corresponding to light contrasting. An arithmetic operation of the length of time at which shade is generated is performed based on the electrical signal; and accordingly, various kinds of dimensions of the object to be measured are calculated and are outputted. In either of the above methods, a dimension measuring range is defined by the width of the parallel light which is emitted from the projector and is received by the optical receiver.
When a user installs a projector and an optical receiver on a base, the user is required to coincide optical axes of the projector and the optical receiver correctly in a direction perpendicular to and in a direction horizontal to the base. Conventionally, in order to make the optical axes coincide, the level of coincidence of the optical axes is displayed on a display screen of a controller connected to the projector and the optical receiver or a personal computer (PC) connected to the controller, and the user adjusts the optical axes while watching the display screen (for example, Japanese Unexamined Patent Publication No. 2008-275462).
With the above-described method which confirms the level of coincidence of the optical axes on the PC or on the controller connected to the projector and the optical receiver, the user cannot intuitively comprehend how large or in which direction an optical axis deviation is specifically generated. Furthermore, in the case where the controller and the PC are installed at a position apart from the projector and the optical receiver, work of optical axis adjustment is very inconvenient and, as a result, a large number of working man-hours are inevitably required.
One way to prevent such a problem from occurring is to increase the density of an amount of light which is projected so that a light projecting spot by the projector can be seen by a human eye. However, in the case of the above-described CCD method, the distance between a light source and the light projecting lens needs to be separated to make parallel light with high accuracy; and therefore, the increase in the density of an amount of light has limitations. Furthermore, even in the case of the scanning method, when the density of an amount of light is largely increased to enhance visibility, there arise other problems such as a safety hazard and degradation of life span of the light source. Thus, it is impractical to increase the density of an amount of light to the point where the light projecting spot can be seen by the human eye.
In addition, apart from the above problems, even if the optical axes of the projector and the optical receiver are made to coincide accurately, contamination or the like is sometimes attached to a light projecting surface and a light receiving surface according to a use environment of a user. In the case where contamination or the like is attached to the light projecting surface of the projector and the light receiving surface of the optical receiver, fluctuation of an amount of received light is generated regardless of a state where an object to be measured is not present; and therefore, there is a problem in that accidental erroneous measurement could occur and it is difficult for the user to understand what has happened. Even if the size of contamination is very small, when an edge due to the contamination which should not be originally present is detected, a measured value is outputted as a value which is far from a dimension value of an actual object to be measured. Moreover, even if the user sees the outputted measured value, the user cannot intuitively determine whether or not the outputted measured value is a dimension value of the actual object to be measured, whether or not contamination is attached to the light projecting surface or the light receiving surface, whether or not there is a problem in the use environment, and the like. Therefore, the light projecting surface of the projector and the light receiving surface of the optical receiver must be cleaned periodically so as to obtain an appropriate dimension measured value.